1. Field of the Invention
The present invention relates to a hydrogen storage alloy electrode capable of reversibly electrochemically storing and discharging hydrogen. More particularly, the present invention relates to a hydrogen storage alloy negative electrode of the sintered type and a manufacturing method of the same.
2. Description of the Prior Art
In recent advances of electronic technology, development of compact and lightweight high performance secondary batteries of higher energy density is strongly required as a power source for portable cordless electronic equipment. In such requirement, metal hydride batteries using a hydrogen storage alloy negative electrode has been particularly noticed as a more environmentally clean energy source rather than lead-acid, nickel-cadmium or other batteries.
A conventional hydrogen storage alloy negative electrode of the non-sintering type for alkaline cells is manufactured by the steps of mixing powdered hydrogen storage alloy materials with binder agents such as polyethylene oxide, polyvinyl alcohol or the like and coating a slurry of the mixture on a conductive core plate such as a perforated (punched) metal plate. In the hydrogen storage alloy negative electrode, the binder agents must be interposed between particles of the hydrogen storage alloy materials and between the hydrogen storage alloy and the conductive core plate to retain the hydrogen storage alloy on the conductive core plate. The discharge characteristics and capacity of the hydrogen storage alloy negative electrode are deteriorated due to insulation resistance of the binder agents.
To solve the problem, there has been proposed a manufacturing method of a hydrogen storage alloy negative electrode of the sintering type, for example, in Japanese Patent Publication No. 58(1983)-46827, Japanese Patent Laid-open Publication No. 2(1990)-12765, etc. The manufacturing method disclosed therein comprises the steps of mixing powdered hydrogen storage alloy materials with powders of precursor materials, such as Co, Ni, TiNi.sub.x and the like, subjecting the mixture of the powder materials placed on a perforated metal plate to a compaction process and sintering the mixture on the metal plate in a vacuum or an inert environment to provide a sintered hydrogen storage alloy negative electrode of higher strength.
In the manufacturing process of the negative electrode, however, when the hydrogen storage alloy materials containing a measured amount of manganese are sintered after being mixed with the powders of Co, Ni, TiNi.sub.x, the manganese melts out of the hydrogen storage alloy, resulting in degradation of the composition of the hydrogen storage alloy. This decreases the discharge capacity of the negative electrode.